1. Field of the Invention
This invention relates to rigid polyurethane foams having physical properties which result in constant or slightly decreasing strain with an increasing stress in compression. Further, this invention relates to a method of shoring up a geological formation which comprises employing these rigid foams and interposing these foams over a support between those geological formation areas which are to be shored up.
2. Description of the Prior Art
U.S. Pat. No. 4,114,382 teaches a method of consolidating geological formations by applying a polyurethane reaction system to the material to be consolidated. This reaction system comprises a polyisocyanate component and a polyol component wherein the polyol component contains about 50:50 weight percent of a polyether having an OH number under about 100 and about 95:5 percent by weight of a polyol selected from the group consisting of those having 2 to 4 hydroxyl groups with a molecular weight of about 62 to 200 and a polyether polyol having an OH number about 200 to 1056 with a molecular weight of about 106 to 1000.
U.S. Pat. No. 4,452,551 teaches a process for stabilizing rock and coal formation by use of a polyurethane forming mixture which employs as the polyol component a mixture comprising polyether polyol having a hydroxyl number of 390 to 580 and having a functionality of 3 to 8 hydroxyl groups with a difunctional polyol having a hydroxyl number of 200 to 300 and from 0 to 100 parts by weight of a flexibilizing agent having a hydroxyl number of 50 to 200.
U.S. Pat. No. 4,454,252 teaches a method of sealing and consolidating water bearing geological formations by reacting a polyisocyanate in equal volume with a polyol, the polyol having a molecular weight between 400 and 600 and a hydroxyl number between 340 and 400 in the presence of an accelerator and a foam stabilizer. None of the prior art teaches the employment of a rigid polyurethane foam system which exhibits nearly constant strain with increasing stress in compression by employing an effective amount of a polyol which is an ethylene oxide-propylene oxide adduct of a toluenediamine isomer mixture.
The subject invention relates to a rigid polyurethane foam which exhibits nearly constant strain with increasing stress in compression. This rigid foam is the reaction product of a mixture of polyether polyols and organic polyisocyanates, a catalyst and a silicone surfactant wherein said polyol mixture comprises an effective amount of an oxyalkylated toluenediamine polyol having a structure of ##STR1## wherein w, x, y, and z represent numerals from 0 to 2; a, b, c, and d represent numerals from 1 to 5; w+x+y+z is from 2 to 5; a+b+c+d is from 2 to 5 and wherein w+x+y+z+a+b+c+d is not less than 5 nor more than 9 and a polyether polyol having a functionality from 2 to 8 and a molecular weight range from 200 to 1000. This rigid polyurethane foam may be advantageously employed for shoring up a geological formation and in equalizing the strain with increasing stress and compression of any such condition by placing a layer of said rigid foam between the imposing force and the resisting force.